The present invention relates to a non-aqueous electrolyte, a solid electrolyte, lithium secondary batteries, and electrochemical capacitors; and, more particularly, the invention relates to an improvement in the diffusivity of electrolyte and a solid electrolyte, to the improvement in load performance of batteries and polymer secondary batteries at a low temperature, and to improvement in the charge-discharge performance of electrochemical capacitors.
A non-aqueous electrolyte using an organic solvent has a high anti-oxidant performance in comparison with an aqueous electrolyte; and, a non-aqueous electrolyte is widely used for lithium primary batteries and lithium secondary batteries, which are driven with a voltage higher than the oxidation voltage of water, as well as for electrochemical capacitors exceeding the 2V class, and the like. Generally, for a non-aqueous electrolyte, organic solvents of a cyclic and linear chain carbonate ester, such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and the like; a cyclic and linear chain ether, such as dimethoxy methane, 1,2-dimethoxy ethane, digryme, trigryme, 1,3-dioxolane, tetrahydrofuran, 2-methyl tetrahydrofuran, and the like; xcex3-butylolactom, sulfolane, methyl propionate, ethyl propionate, and others are used. However, these solvents have a larger molecular weight in comparison with a water molecule, and so disadvantages result due to solubility and dissociation, because the number of molecules of the solvent is small in an equivalent salt concentration. Furthermore, the diffusivity of ions is decreased, because the volume of solvation to ions becomes larger than water, and a decreasing capacity performance of batteries and capacitors is generated at a low temperature or high rate load with the non-aqueous electrolyte.
A solid electrolyte, which is formed by impregnating a non-aqueous electrolyte into a foamed polymer material, such as polyvinylidene fluoride (hereinafter, called as PVDF) and the like, and a gel group solid polymer electrolyte, which uses a gel formed by the steps of melting a polymer such as polyethylene oxide (hereinafter, called as PEO) with a non-aqueous electrolyte at a high temperature and cooling the mixture to room temperature as an electrolyte, makes it possible to make the outer container of the batteries thin and light weight, because the electrolyte creates no problems concerning liquid. leakage in the batteries, nor the necessity to use a strong battery can. Therefore, currently, polymer batteries using these electrolytes have been developed and have come to be mounted in portable telephones and the like. These polymer electrolytes have an even lower diffusivity of ions in comparison with liquid non-aqueous electrolytes, and their operation performance at a low temperature and high rate load is further decreased.
A non-aqueous electrolyte has a low electric conductivity in comparison with an aqueous electrolyte and is inferior to the aqueous electrolyte in low temperature characteristics and load characteristics. In order to solve such problems, U.S. Pat. No. 5,795,677 discloses a non-aqueous electrolyte which includes a fluorinated ether having a structure in which a fluorinated alkyl chain and ether oxygen are connected via a xe2x80x94CH2xe2x80x94 structure. In accordance with the above prior art, the low temperature characteristics and load characteristics are certainly improved by mixing the fluorinated solvent.
However, in the case of the above prior art, wherein the fluorinated alkyl chain and ether oxygen are connected via a xe2x80x94CH2xe2x80x94 structure, the decrease in the electron density on the ether oxygen is small, and an interaction between the fluorinated ether and lithium ions is produced. Therefore, the fluorinated ether is solvated with lithium ions, and an advantage in which the improvement in diffusivity of lithium ions produced by mixing the fluorinated solvent can not be achieved sufficiently.
One of the objects of the present invention is to provide a non-aqueous electrolyte having a high diffusivity; a polymer electrolyte having a high diffusivity; and non-aqueous electrolyte group batteries, electrochemical capacitors, and polymer secondary batteries, the performance at a low temperature of which is improved by using the above electrolyte.
The above object can be achieved by mixing a fluorinated solvent indicated by a chemical formula 1 into the non-aqueous electrolyte. If lithium salt is used as a supporting electrolyte of the non-aqueous electrolyte, the electrolyte can be used as the electrolyte for lithium primary battery and a lithium secondary battery, and the diffusivity of the lithium ions can be improved. Furthermore, the performance of these batteries at a low temperature can be improved by using such an electrolyte. If quaternary onium salt is used as a supporting electrolyte, the electrolyte can be used as the electrolyte for electrochemical capacitors, and the performance of these capacitors at a low temperature can be improved by using the electrolyte. Furthermore, the diffusivity of lithium ions in a polymer electrolyte can be improved by mixing the fluorinated solvent expressed by the chemical formula 1 into a polymer electrolyte composed of a mixture of a polymer compound and a non-aqueous electrolyte, and the performance of the polymer secondary batteries at a low temperature can be improved by using the electrolyte.
The fluorinated solvent to be mixed into an electrolyte is ethyl ether of fluorinated alkyl carboxylic acid, the terminal end of the fluorinated alkyl of which is a difluoromethyl group, expressed by the following chemical formula 5, which has a structure in which the fluorinated alkyl group is directly combined with functional group: 
(wherein, s indicates any one of integers of 0, 3, 5, 7, and 9), or
fluorinated alkyl iodide, the terminal end of the fluorinated alkyl of which is a difluoromethyl group, expressed by the following chemical formula 6: 
(wherein, t indicates any one of integers of 1, 3, and 5), or
fluorinated solvent, in which both terminal ends of its molecule are isoheptafluoropropyl groups, expressed by the following chemical formula 7: 
(wherein, u indicates an integer of 4 or 8), or
fluorinated alkyl acrylate compound, the terminal end of the fluorinated alkyl of which is a difluoromethyl group, expressed by the following chemical formula 8: 
(wherein, v indicates any one of integers of 4, 6, 8, and 10), or
fluorinated alkyl methacrylate compound, the terminal end of the fluorinated alkyl of which is a difluoromethyl group, expressed by the following chemical formula 9: 
(wherein, w indicates any one of integers of 4, 6, 8, and 10), or
a compound expressed by the following chemical formula 10: 
(wherein, n indicates an integer in the range of 2-6, and R4 indicates any one of methyl group, ethyl group, and propyl group), for instance, any one of ether of H(CF2)2OCH3, H(CF2)2OCH2CH3, H(CF2)2OCH2CF3, and the like, or ether of CF3CHFCF2OCH3, CF3CHFCF2OCH2CH3, or iso-perfluoroalkyl alkyl ether expressed by the chemical formula 4, that is, 2-trifluoromethyl hexafluoropropyl methyl ether, 2-trifluoromethyl hexafluoropropyl ethyl ether, 2-trifluoromethyl hexafluoropropyl propyl ether, 3-trifluoro octafluorobutyl methyl ether, 3-trifluoro octafluorobutyl ethyl ether, 3-trifluoro octafluorobutyl propyl ether, 4-trifluorodecafluoropenthyl methyl ether, 4-trifluorodecafluoropenthyl ethyl ether, 4-trifluorodecafluoropenthyl propyl ether, 5-trifluorododecafluorohexyl methyl ether, 5-trifluorododecafluorohexyl ethyl ether, 5-trifluorododecafluorohexyl propyl ether, 6-trifluorotetradecafluoroheptyl methyl ether, 6-trifluorotetradecafluoroheptyl ethyl ether, 6-trifluorotetradecafluoroheptyl propyl ether, 7-trifluorohexadecafluorooctyl methyl ether, 7-trifluorohexadecafluorooctyl ethyl ether, and 7-trifluorohexadecafluorohexyl octyl ether can be used. Furthermore, a mixture of any one of the above compounds with perfluoroalkyl alkyl ether having a linear chain structure can be used.
The solvent for composing the electrolyte other than the fluorinated solvent are a cyclic and linear chain carbonate ester, such as ethylene carbonate, propylene carbonate, butylene carbonate, chloroethylene carbonate, trifluoromethyl propylene carbonate, vinylene carbonate, dimethyl vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and the like; cyclic and linear chain ether such as dimethoxy methane, 1, 2-dimethoxy ethane, digryme, trigryme, 1, 3-dioxolane, tetrahydrofuran, 2-methyl tetrahydrofuran, and the like; xcex3-butylolactom, sulfolane, methyl propionate, ethyl propionate, ethylene sulfate, dimethyl sulfoxide, ethyl methyl sulfoxide, diethyl sulfoxide, methyl propyl sulfoxide, ethyl propyl sulfoxide, propane sulton, and others, which can be used alone or as a mixture.
As the lithium salt for a supporting electrolyte of the electrolyte for lithium battery, LiPF6, LiBF4, LiClF4, LiSO3CF3, LiN(SO2CF3), LiN(SO2CF2CF3), LiC(SO2CF2CF3)3, LiC(SO2CF3)3, LiI, LiCl, LiF, LiPF5(SO2CF3), LiPF4(SO2CF3)2, and the like can be used.
As the supporting electrolyte for an electrochemical capacitor, quaternary onium salts such as (CH3CH2)4NBF4, (CH3CH2)4NPF6, (CH3CH2)4NClO4, (CH3CH2)4PBF4, (CH3CH2)4PPF6, (CH3CH2)4PClO4, (CH3)4PBF4, (CH3)4PPF6, (CH3)4PClO4, (CH3CH2CH2)4PBF4, (CH3CH2CH2)4PPF6, (CH3CH2CH2)4PClO4, (CH3CH2CH2)4NBF4, (CH3CH2CH2)4NPF6, (CH3CH2CH2)4NClO4, (CH3)4NBF4, (CH3)4NPF6, (CH3)4NClO4, (CH3CH2CH2CH2)4PBF4, (CH3CH2CH2CH2)4PPF6, (CH3CH2CH2CH2)4PClO4, (CH3CH2CH2CH2)4NBF4, (CH3CH2CH2CH2)4NPF6, (CH3CH2CH2CH2)4NClO4, (CH3CH2)4NSO2CF3, (CH3CH2)4NN(SO2CF3)2, (CH3CH2)4NSO3C4F9, (CH3CH2)4NB(CH3CH2)4, and the like can be used. When carbon material is used as the active material, the charging capacity can be increased by utilizing concurrently the intercalation reaction of lithium ions. Therefore, the lithium salt indicated for a lithium battery can be used as the electrolyte for the electrochemical capacitors.
(Polymer Electrolyte)
The polymer electrolyte can be manufactured by mixing, or heating to dissolve together and cooling, the electrolyte containing the above fluorinated solvent with an appropriate amount of polymer such as polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, and the like. Otherwise, the polymer electrolyte can be manufactured by impregnating the electrolyte containing the above fluorinated solvent into a foamed polymer base material such as polyvinylidene fluoride, polyurethane, and the like. Otherwise, the polymer electrolyte can be manufactured by mixing the electrolyte containing the above fluorinated solvent with a monomer, or an oligomer of methacrylic acid derivative having double bond therein, and curing by heating the mixture. As the non-aqueous electrolyte to be mixed with the above monomer, or oligomer, the electrolyte for the lithium battery described above can be used.
(Lithium Primary Battery)
The lithium primary battery used in accordance with the present invention can be manufactured by using a lithium metal as a negative electrode; using a fabricated pellet of manganese dioxide as a positive electrode of a coin type battery, or using manganese dioxide applied onto both side planes of aluminum foil as a positive electrode, which is laminated with a lithium metal foil negative electrode via a polymer separator and is wound to form an electrode group; and inserting the electrode group into a cylindrical battery can to form a cylindrical battery by sealing.
Furthermore, in addition to metallic lithium, the negative electrode can be formed with a material which can intercalate-deintercalate lithium, for instance, a lithium-aluminum alloy, carbon material, for example, cokes, graphite, and the like. In addition to manganese dioxide, the positive electrode can be formed with an oxide containing at least one of metallic materials such as cobalt, nickel, niobium, vanadium, and the like.
(Lithium Secondary Battery)
As the negative electrode of the lithium secondary battery, metallic lithium; an alloy of lithium with aluminum; natural or artificial graphite and amorphous carbon materials; or complex materials of carbon with a material such as silicon, germanium, aluminum, gold, and the like, which form an alloy with lithium, can be used.
As materials for the positive electrode, a complex oxide of lithium with cobalt, nickel, iron, and the like; a material obtained by adding any of the transition metals, silicon, germanium, aluminum, manganese, magnesium, and the like to the above complex oxide, and lithium manganate and a material obtained by adding and mixing any of lithium, transition metals, silicon, germanium, aluminum, manganese, magnesium, and the like, to lithium manganate; can be used. As a material for the separator, a micro-porous film of a polymer such as polyethylene, polypropylene, vinylene copolymer, butylene, and the like, or a micro-porous film obtained by laminating the above film to two layers, or three layers can be used.
(Polymer Secondary Battery)
A polymer secondary battery can be formed by interposing the above polymer electrolyte and lithium between the negative electrode and the positive electrode, which can intercalate-deintercalate lithium. Otherwise, the polymer electrolyte can be used by being impregnated into micro-porous film made of polyethylene, polypropylene, polybutene, and the like. The negative electrode and the positive electrode described in connection with the above lithium secondary battery can be preferably used.
(Electrochemical Capacitor)
The electrochemical capacitor is formed, using a carbon material having a large specific surface area as polarizable electrodes of the positive electrode and the negative electrode, by laminating or winding these electrodes via a separator, and pouring an electrolyte. The electrolyte can be used as a gel state polymer electrolyte by mixing a polymer, in addition to a liquid electrolyte. As the polarizable carbon material having a large specific surface area, glassy carbon, carbon black, carbon fiber, activated carbon micro-bead, activated carbon fiber, and the like can be used. In addition to the above carbon material, organic compounds such as pyrrole compounds, and aniline group compounds can be used as the polarizable electrode material. As the separator, the material described previously can be used.